1. Field of the Invention
The present invention relates to a fuel supply pump and a manufacturing method of a housing of the fuel supply pump.
2. Description of Related Art
With reference to FIG. 5, a prior art fuel supply pump 100 includes a plunger 101, a cylinder body 103 and a plunger drive mechanism (not shown). The plunger 101 is adapted to reciprocate in an axial direction thereof. The cylinder body 103 includes a cylinder hole 102, which receives the plunger 101 in an axially slidable manner. The plunger drive mechanism (not shown) converts a rotational motion, which is transmitted from an internal combustion engine (not shown), into a linear motion and conducts the linear motion to the plunger 101. The fuel supply pump 100 is applied to an accumulator type fuel injection system, which injects high pressure fuel having a pressure of more than 100 MPa into the internal combustion engine through a common rail.
Furthermore, in the fuel supply pump 100, one axial end portion of the cylinder hole 102 is fluid-tightly closed (partitioned) by the plunger 101 to form a pressurizing chamber 104, in which fuel is pressurized. In the fuel supply pump 100, the plunger 101, which is axially slidably received in the cylinder hole 102, is axially reciprocated to change a volume of the pressurizing chamber 104, so that the fuel is drawn into the pressurizing chamber 104 and is then discharged from the pressurizing chamber 104 upon pressurization of the fuel in the pressurizing chamber 104.
Specifically, a discharge flow passage 106 is connected to the pressurizing chamber 104 to discharge the pressurized fuel from the pressurizing chamber 104, and a connection opening 107 of the discharge flow passage 106 is formed in a hole wall (an inner peripheral wall) of the cylinder hole 102, which forms the pressurizing chamber 104. Furthermore, a check valve 108 is placed in the discharge flow passage 106 to limit a backflow of the fuel toward the pressurizing chamber 104. When the pressure of the fuel in the pressurizing chamber 104 becomes larger than a predetermined valve opening pressure, the check valve 108 is opened, so that the fuel, which is pressurized in the pressurizing chamber 104, is guided to an outside of the fuel supply pump 100 through the discharge flow passage 106. In this way, the fuel, which is pressurized in the pressurizing chamber 104, is discharged to the outside of the fuel supply pump 100 through the discharge flow passage 106 and is then supplied to the common rail.
In the fuel supply pump 100, a stress load is repeatedly and intensively applied to an inner peripheral edge 109 of the connection opening 107 and an area adjacent to the inner peripheral edge 109 upon repeating of increasing and decreasing the fuel pressure in the pressurizing chamber 104. Therefore, it is required to increase the pressure resistance at the inner peripheral edge 109 of the connection opening 107 and the area adjacent to the inner peripheral edge 109.
It has been proposed to increase the pressure resistance by applying a residual compression stress through autofrettage. Specifically, It is known to apply the technique of autofrettage to a common rail or a fuel injector of an accumulator fuel injection system (see, for example, DE102006054440B3 corresponding to US2010/0154501A1).
Therefore, it may be conceivable to increase the pressure resistance at the inner peripheral edge 109 of the connection opening 107 and the area adjacent to the inner peripheral edge 109 by applying the technique of the autofrettage thereto.
However, the inner peripheral edge 109 is formed in a hole wall of the cylinder hole 102, which has been processed to have a high hardness through, for example, a carburizing process, a nitriding process or a hardening process (a quenching process) to meet a requirement of having a seizing resistance against the slide contact of the plunger 101 to the hole wall of the cylinder hole 102. Therefore, even when the pressure is applied to the hole wall of the cylinder hole 102 to increase the pressure resistance at the inner peripheral edge 109 and the area adjacent to the inner peripheral edge 109 through the autofrettage, it is difficult to apply the residual compression stress to the inner peripheral edge 109 and the area adjacent to the inner peripheral edge 109. Thereby, it is not possible to increase the pressure resistance at the inner peripheral edge 109 and the area adjacent to the inner peripheral edge 109.